High electron mobility transistors (HEMTs) are common types of solid state transistors that are fabricated from semiconductor materials such as indium phosphide (InP) or gallium arsenide (GaAs). For example, GaAs has become the standard for signal amplification in civil and military radar, handset cellular, and satellite communications. GaAs has a higher electron mobility and a lower source resistance than Si, which allows GaAs based devices to function at higher frequencies. However, GaAs has a relatively small bandgap (1.42 eV at room temperature) and relatively small breakdown voltage, which prevents GaAs based HEMTs from providing high power at high frequencies.
Improvements in the manufacturing have focused interest on the development of gallium nitride (GaN) and aluminum gallium nitride (AlGaN) semiconductor materials to form planar AlGaN/GaN based HEMT devices. These devices can generate large amounts of power because of their unique combination of material characteristics including high breakdown fields, wide bandgaps (3.36 eV for GaN at room temperature), large conduction band offset, and high saturated electron drift velocity.
For example, a conventional 1.7 mm×1.7 mm GaN based HEMT can generate 2.2 W/mm of power and have a noise figure of less than 1 dB for the 0.2 to 8 GHz frequency range. These conventional GaN based HEMTs, however, suffer from defect density problems and self-heating issues.
Thus, there is a need to overcome these and other problems of the prior art and to provide GaN nanowire based and larger, GaN post-based HEMTs.